Integrated method and structure for in-situ hydrogen production from coal seams and coalbed methane exploitation

ABSTRACT

The application discloses an integrated method and structure for in-situ hydrogen production from coal seams and coalbed methane exploitation, belonging to the technical field of energy exploitation. The method comprises: injecting gasification agent through an injection well, exploiting coalbed methane and gasification gas through a production well. The injection well is a stepped horizontal well, the injection well is provided with at least one, and the projections of the horizontal sections of any two injection wells in the vertical direction do not overlap. At least one horizontal section of the stepped horizontal well is arranged in any coal seam to be mined. The method of the present application avoids the large-area continuous gasification of a single coal seam and the repeated position gasification of overlapping multiple coal seams, reduces the change range and degree of formation stress, disperses the underground void volume, reduces the risk of formation or ground collapse.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese Application Serial No. 202111225237.6, filed on Oct. 21, 2022. The content of the aforementioned application, including any intervening amendments thereto, is incorporated herein by reference.

TECHNICAL FIELD

The present application relates to the technical field of energy exploitation, in particular to an integrated method for in-situ hydrogen production from coal seams and coalbed methane exploitation and a structure for integrated exploitation using the method.

BACKGROUND

Underground coal gasification (UCG) refers to the controlled combustion of underground coal to generate combustible gas through thermal and chemical effects on coal. This technology can not only recover coal resources abandoned in mines, but also can be used for thin coal seams, deep coal seams, high sulfur, high ash, and high gas concentration coal seams that are difficult to mine or with poor economic and safely mining. It has good economic and environmental benefits, and improves the utilization rate and utilization level of coal resources.

For underground coal seams, it usually has not only coal resources, but also associated coalbed methane (CBM). Coalbed methane is an important unconventional natural gas resource whose main component is methane. Therefore, under the current condition of mature UCG technology, existing technicians try to achieve the purpose of integrated mining by combining UCG technology and CBM production technology.

For example, Chinese patent CN112081558A discloses a collaborative mining method, structure and construction method of underground coal gasification and coalbed methane. The patent uses multiple U-shaped wells consisting of one vertical well and one or more Multiple-branch horizontal wells as the production structure. Through the method of underground gasification of the lower coal seam and coalbed methane mining of the upper coal seam, the cooperative mining of coalbed methane and coal gasification gas increases the mining efficiency. However, this technology has the following problems: since the technology uses multiple U-shaped wells, and gasification is performed in the horizontal sections of the multiple U-shaped wells, the multi-layer gasification sections are on the same vertical plane. After gasification, the coal seam is deficient and the pressure is reduced, which is easy to cause the formation of this section to be unstable, prone to accidents, and has low safety.

SUMMARY

In view of the deficiencies of the prior art, an object of the present application is to provide an integrated method for in-situ hydrogen production from coal seams and coalbed methane exploitation, which has high safety while realizing the simultaneous production of coalbed methane and coal gasification gas.

In order to achieve the above object, the present application adopts the following technical solutions: an integrated method for in-situ hydrogen production from coal seams and coalbed methane exploitation, comprising the following steps:

injecting gasification agent through an injection well, and exploiting coalbed methane and gasification gas through a production well;

wherein the injection well is configured to be a stepped horizontal well, the injection well is provided with at least one, and the projections of the horizontal sections of any two injection wells in the vertical direction do not overlap, and at least one horizontal section of the stepped horizontal well is arranged in any coal seam to be mined.

An embodiment of the present application is that the production well is configured to be a cluster well, and the directional well or the first vertical well of the cluster well is configured to pass through all the coal seams to be mined.

An embodiment of the present application is that the production well is a combination of a plurality of second vertical wells or inclined wells, and the second vertical wells or inclined wells are configured to pass through all the coal seams to be mined.

An embodiment of the present application is that a vertical well or inclined well passing through the coal seam to be mined where the horizontal section is located is provided in the coal gasification range of the horizontal section, and the horizontal section communicates or does not communicate with its adjacent vertical well or inclined well.

An embodiment of the present application is that before injecting the gasification agent into the injection well and exploiting the coalbed methane and gasification gas through the production well, the method further comprises: draining water from the coal seam through the production well.

An embodiment of the present application is that multi-layered coal seams to be mined are simultaneously injected with a gasification agent and gasified simultaneously; or, starting from the lowest coal seam to be mined, the gasification agent is injected upward layer by layer and gasified in stages.

An embodiment of the present application is that after injecting gasification agent into the injection well, and after exploiting coalbed methane and gasified gas in the production well, the method also comprises: carrying out carbon dioxide separation on the ground from the mined coalbed methane and gasification gas, and injecting separated carbon dioxide into the target coal seam.

An embodiment of the present application is that the carbon dioxide is injected into a target coal seam through an injection well far from the horizontal section in the target coal seam.

Another object of the present application is to provide an integrated structure for in-situ hydrogen production from coal seams and coalbed methane exploitation, the integrated exploitation structure comprising,

an injection well, which is provided with at least one and is configured to be a stepped horizontal well, wherein the projections of the horizontal sections of any two injection wells in the vertical direction do not overlap, and at least one horizontal section of the stepped horizontal well is arranged in any coal seam to be mined;

a production well, which is configured to pass through all the coal seams to be mined, and for any horizontal section of the injection well, there is a production well that passes through the coal gasification range of the coal seam where the horizontal section is located.

An embodiment of the present application is that the production well is configured to be a cluster well, and a directional well or a first vertical well of the cluster well is configured to pass through all the coal seams to be mined; or, the production well is a combination of a plurality of second vertical wells or inclined wells, and the second vertical wells or inclined wells are configured to pass through all the coal seams to be mined.

The beneficial effects of this application are:

(1) Integration of coalbed methane exploitation and in-situ hydrogen production from coal, and simultaneous exploitation of multiple resources.

(2) Simultaneous exploitation of multiple coal seams, mining of coalbed methane, and hydrogen production from coal.

(3) Hydrogen production also realizes CO2 sequestration, realizes zero carbon emission, and protects the environment.

(4) Save the land area on the ground, only two well sites can realize the exploitation of multiple coal seams and multiple gasification locations.

(5) Large-area continuous gasification of a single coal seam and gasification of overlapping multiple coal seams are avoided, reducing the range and degree of change in formation stress, dispersing the underground void volume, and reducing the risk of formation or ground collapse.

(6) The combination of mining methods is diverse, adapting to different exploitation needs.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of the integrated exploitation structure according to Embodiment 1;

FIG. 2 is a schematic diagram of the integrated exploitation structure according to Embodiment 1 when draining water;

FIG. 3 is a schematic diagram of the integrated exploitation structure according to Embodiment 1 when mining coalbed methane;

FIG. 4 is a schematic diagram of the integrated exploitation structure according to Embodiment 1 when coal is gasified and carbon dioxide is reinjected;

FIG. 5 is a schematic diagram of the integrated exploitation structure according to Embodiment 2 when coalbed methane is mining and coal gasification are performed on a single coal seam at the same time;

FIG. 6 is a schematic diagram of the integrated exploitation structure according to Embodiment 3 when mining coalbed methane;

FIG. 7 is a schematic diagram of the integrated exploitation structure according to Embodiment 3 when coal gasification is simultaneously performed on 3 coal seams;

FIG. 8 is a schematic diagram of an integrated exploitation structure according to Embodiment 4;

FIG. 9 is a schematic diagram of the integrated exploitation structure according to Embodiment 4 when mining coalbed methane;

FIG. 10 is a schematic diagram of the integrated exploitation structure according to Embodiment 4 when coal gasification is performed on a single coal seam.

1. Coal seam to be mined 2. Interlayer 3. Injection well 4. Production well, 5. Coal gasification range 31. First horizontal section 32. Second horizontal section, 33. Third horizontal section 41. Well No. 1 42. Well No. 2, 43. Well No. 3 44. Second vertical well.

DETAILED DESCRIPTION

In order to make the technical solutions and technical advantages of the present application clearer, the technical solutions in the implementation process of the present application will be clearly and completely described below with reference to the embodiments and the accompanying drawings.

In the present application, the gasification agent refers to the necessary medium in the coal gasification process, usually water vapor, oxygen and the like.

In the present application, the gasification gas refers to the gas generated by a series of chemical reactions of coal underground under the action of gasification agent, and its main components are CH4, H2, CO, CO2 and so on.

In the present application, the stepped horizontal well refers to a special horizontal well that includes a plurality of deflection sections and horizontal sections, and a deflection section is provided between adjacent horizontal sections.

In the present application, the first vertical well refers to a cluster well, which includes a vertical well and a plurality of directional wells, and the first vertical well refers to a vertical well in a cluster well.

In the present application, the second vertical well refers to when the injection well is a combination of multiple vertical wells or inclined wells, the second vertical well is a vertical well in the combination of multiple vertical wells or inclined wells.

In the present application, the projection in the vertical direction refers to the projection of the three-dimensional graphics on the horizontal plane with the vertical direction as the projection path.

In the present application, the “coal gasification range” refers to: injecting gasification agent through the horizontal section of the stepped horizontal well and gasifying coal within a certain range of the horizontal section, this range refers to the “coal gasification range”, and the names such as “effective gasification range” and “underground gasifier” are also used in industry.

An integrated method for in-situ hydrogen production from coal seams and coalbed methane exploitation, comprising the following steps:

injecting gasification agent through an injection well 3, and exploiting coalbed methane and gasification gas through a production well 4;

wherein the injection well 4 is configured to be a stepped horizontal well, the injection well 4 is provided with at least one, and the projections of the horizontal sections of any two injection wells 4 in the vertical direction do not overlap, and at least one horizontal section of the stepped horizontal well is arranged in any coal seam to be mined 1.

For the multi-layered coal seam 1 to be mined, its distribution is usually as shown in FIG. 1 . The interlayer 2 or cap layer separates two adjacent coal seams 1 to be mined, and the interlayer 2 or cap layer is usually a tight rock layer such as mudstone, mud shale or sandstone. When it is mined, staged mining and gasification are required.

In the present application, a stepped horizontal well is used as the injection well 3 for injecting the gasification agent, and each coal seam 1 to be mined is provided with at least one horizontal section of the stepped horizontal well. Since coal gasification usually occurs in the horizontal section, this ensures that each coal seam 1 to be mined can undergo coal gasification. At the same time, in order to avoid that the coal gasification sections of the coal seams 1 to be mined are all on the same vertical plane, it is defined that the projections of any two horizontal sections on the horizontal plane do not overlap. In this way, the vertical difference of each coal gasification section is guaranteed to the greatest extent. Even if a certain layer of coal seam to be mined has a deficit due to coal gasification, it will not cause formation collapse, and the safety is better.

In some embodiments, due to the wide distribution area of a single-layer coal seam in the lateral direction, it is difficult to achieve maximum mining by using only one stepped horizontal well. Therefore, multiple stepped horizontal wells can be set up, multiple horizontal sections can be set in the same coal seam to be mined, and each horizontal section is separated by a certain distance, and the distance can be determined according to the length of the horizontal section and the gasification area.

As for the production well 4, because it has the functions of both coalbed methane mining and gasification gas mining, there is always a production well 4 passing through the coal gasification range 5 of a horizontal section. The applicant realizes that, since the coal is burned during the coal gasification process, when the pressure of the coal seam increases, new cracks will be formed in the coal seam, and the permeability will also increase. Therefore, it is only necessary to set the horizontal section and the production well 4 in the coal seam 1 to be mined within a certain distance range, and the exploitation of gasification gas and coalbed methane can be realized, and there is no need to connect the horizontal section and the production well 4, which enables production Costs are greatly reduced.

In some embodiments, the production wells 4 are cluster wells, and the directional or first straight wells of the cluster wells pass through all the coal seams to he mined. Cluster wells are well groups that include a first vertical well and multiple directional wells. Only one well site can realize the exploitation of multiple production points, saving production costs. Meanwhile, for the cluster well, within the coal gasification range of each horizontal section of the injection well 3, there is a first vertical well or directional well that passes through the cluster well of the coal seam where the horizontal section is located.

In some embodiments, the production well 4 is a combination of a plurality of second vertical wells 44 or inclined wells, and the second vertical wells 44 or inclined wells pass through all the coal seams 1 to be mined. Since cluster wells have slightly higher requirements on drilling technology, in some areas where multiple wells can be drilled, the method of directly drilling multiple second vertical wells 44 or inclined wells can be used for mining. Due to the low difficulty of drilling a vertical well, in most cases, multiple second vertical wells 44 can be drilled. Within the coal gasification range 5 of each horizontal section of the injection well 3, there is a second vertical well 44 or inclined well penetrating the coal seam where the horizontal section is located.

In some embodiments, before injecting the gasification agent into the injection well 3 and exploiting the coalbed methane and gasification gas through the production well 4, the method further comprises: draining water from the coal seam to be mined 1 through the production well 4. Since the coal seam is usually an aquifer, a large amount of formation water is contained in the coal seam or in the barrier layer of the coal seam. It is necessary to drain the coal seam before mining coalbed methane and gasification gas. Both the injection well 3 and the production well 4 can be used as drainage wells, but usually, the production well 4 is used as the drainage well.

In some embodiments, when the coal in the coal seam to be mined 1 is gasified, the multi-layer coal seam to be mined 1 can be simultaneously injected with a gasification agent and gasified simultaneously. The advantage of this is that it can save production time and save production costs. In other embodiments, starting from the lowest coal seam to be mined 1, the gasification agent can be injected upward layer by layer for gasification. After the current coal seam is gasified and mined, the gasification agent is injected into the upper layer of the coal seam 1 to be mined and gasified. The advantage of this is that it is simpler to operate and requires less equipment and operators.

At the same time, in the above-mentioned embodiment, before the coal is gasified, the coalbed methane can be mined first, and after the coalbed methane is mined, the coal is gasified. The advantage of this is that the entire operation is safer and the mining is more thorough. The coalbed methane can also be mined at the same time as gasification, so that the coalbed methane and the gasification gas can be mined together. The advantage of this operation is that it saves time.

In some embodiments, after the gasification gas and the coalbed methane are generated, the method further includes: separating the carbon dioxide in the coalbed methane and the gasification gas, and injecting the separated carbon dioxide into the target coalbed. Since the gasification gas contains a large amount of carbon dioxide, if the separated carbon dioxide is directly discharged, it will increase the carbon emissions. Therefore, re-injecting the separated carbon dioxide into the formation can both reduce carbon emissions and increase formation pressure. Preferably, in order to fully exert the effect of injecting carbon dioxide into the formation, carbon dioxide is injected into the target coal seam through an injection well far from the horizontal section in the coal seam to be mined 1. In the process of coal gasification, the pressure in the coal seam to be mined 1 increase, but with the continuous exploitation of gasification gas, the pressure in this area gradually decreases. Therefore, injecting carbon dioxide into the coal seam in this way can further drive the coalbed methane toward the area where the horizontal section is located, and the exploitation of the coalbed methane can be more thorough. At the same time, this can also increase the pressure of the coal seam and prevent the coal seam from collapsing due to too low pressure.

Another object of the present application is to provide an integrated structure for in-situ hydrogen production from coal seams and coalbed methane exploitation, comprising:

An injection well 3, which is provided with at least one and is configured to be a stepped horizontal well, wherein the projections of the horizontal sections of any two injection wells 3 in the vertical direction do not overlap, and at least one horizontal section of the stepped horizontal well is arranged in any coal seam to be mined 1;

Specifically, the number of injection wells 3 to be provided is determined according to the lateral distribution area of the coal seam to be mined 1 and the gasification area of each horizontal section. By setting the horizontal section so that the projections in the vertical direction do not overlap, the formation stability after coal gasification is higher, and safety accidents such as collapse are less likely to occur. By arranging at least one horizontal section inside any coal seam to be mined 1, all the coal seams to be mined 1 can be fully mined. Meanwhile, equipment such as an igniter required for coal gasification on each horizontal section belongs to the prior art, so the detailed structure thereof will not be repeated here.

A production well 4, which is configured to pass through all the coal seams to be mined 1, and in the coal gasification range 5 of the coal seam where any horizontal section of the injection well 3 is located, there is a production well 4 passing through the coal seam to be mined 1 where the horizontal section is located.

Specifically, for any horizontal section, within the coal gasification range 5 of the coal seam where the horizontal section is located, there is a production well 4 that passes through the coal seam to be mined where the horizontal section is located. Due to the large range, the precision requirements for drilling are low, so the cost is relatively lower.

For the production well 4, it can be a cluster well, or a combination of a plurality of second vertical wells 44 or inclined wells, but at least one production well 4 passes through all the coal seams 1 to be generated. The more production wells 4 that pass through all the coal seams 1 to be mined, the better the final result.

Embodiment 1

As shown in FIG. 1 , in this embodiment, the cluster wells are used as the production wells 4 and the stepped horizontal wells are used as the injection wells 3 to carry out the integrated exploitation of coal seam in-situ hydrogen production and coalbed methane, and one stepped horizontal well is provided. In this embodiment, there are three layers of coal seams to be mined 1, and adjacent coal seams to be mined 1 are separated by interlayers 2.

In this embodiment, the injection well 3 is provided with three horizontal sections: a first horizontal section 31, a second horizontal section 32 and a third horizontal section 33. The first horizontal section 31 is arranged in the upper coal seam to be mined, the second horizontal section 32 is arranged in the middle coal seam to be mined, and the third horizontal section 33 is arranged in the lower coal seam to be mined. Meanwhile, the projections of the first horizontal section 31, the second horizontal section 32 and the third horizontal section 33 in the vertical direction do not overlap. For the production well 4, it is provided with a first vertical well and two directional wells: the two directional wells are well No. 1 41 and well No. 3 43, respectively, and the first vertical well is well No. 2 42. The well No. 2 42 passes through the coal gasification range 5 of the coal seam to be mined where the second horizontal section 32 is located, the well No. 1 41 passes through the coal gasification range 5 of the coal seam to be mined where the first horizontal section 31 is located, and the well No. 3 43 passes through the coal gasification range 5 of the coal seam to be mined where the third horizontal section 33 is located.

As shown in FIG. 2 , during mining, since these coal seams contain a large amount of coalbed water, cluster wells are first used to drain the coal seam 1 to be mined, and the migration direction of the coalbed water is marked in the figure;

As shown in FIG. 3 , the stepped horizontal wells are used for mining coalbed methane. In this process, cluster wells are used for draining water and mining coalbed methane at the same time, and the migration direction of coalbed methane and coalbed water is marked in the figure;

As shown in FIG. 4 , after the coalbed methane has been exploited or has no economic exploitation value, the gasification agent is injected through the injection well 3: First, inject gasification agent into the lowermost coal seam to be mined and ignite for coal gasification and form coal gasification range 5. In the process of coal gasification, the generated gasification gas is extracted through the well No. 3 43, the extracted gasification gas is subjected to carbon dioxide separation, and the separated carbon dioxide is injected through the well No. 1 31 into the lowest coal seam to be mined. When the gasification in the lower gasification section is completed, the coal in the coal seam to be mined in the middle starts to be gasified, and repeat this process until all three layers of the coal seam to be mined are mined. When the coal in the middle coal seam to be mined is gasified, carbon dioxide is injected into the middle coal seam to be mined through well No. 1 41 or well No. 3 43. When the upper coal seam to he mined is gasified, carbon dioxide is injected into the upper coal seam to be mined through well No. 3 43. The figure shows the direction of gas migration.

Embodiment 2

The difference between the integrated exploitation structure in this embodiment and the first embodiment is the integrated exploitation method.

As shown in FIG. 5 , in this embodiment, the water content of the coal seam 1 to be mined is relatively low, and gas exploitation is directly carried out in the coal seam to be mined 1: First, injecting a gasification agent into the lowest coal seam to be mined and igniting for coal gasification, thereby forming a coal gasification range 5. At the same time, the coalbed methane is mined through the well No. 1 41 and the well No. 2 42, and coalbed methane and gasification gas are exploited through the No. 3 well 43 at the same time. At this time, since the coal gasification process occurs in the lowest coal seam to be mined, a large amount of heat will be generated during the gasification process, which is helpful for the coalbed methane exploitation of the lowest coal seam to be mined and the adjacent coal seams to be mined. After carbon dioxide separation is performed on the mined coalbed methane and gasification gas, the separated carbon dioxide is injected into the lower coal seam to be mined through well No. 1 41. When the coal gasification process in the lower coal seam to be mined is completed and the gasification gas collection is also completed, the upper coal seams to be mined adjacent to the lower coal seam to be mined are sequentially gasified. Repeat this until all three layers of coal seam to be mined have been mined. During the mining process, when the coal in the middle coal seam to be mined is gasified, carbon dioxide is injected into the middle coal seam to be mined through well No. 1 41 or well No. 3 43. When the upper coal seam to be mined is gasified, carbon dioxide is injected into the upper coal seam to be mined through well No. 3 43. The figure shows the direction of gas migration.

Embodiment 3

The difference between the integrated exploitation structure in this embodiment and the first embodiment is the integrated exploitation method.

As shown in FIG. 6 , in this embodiment, firstly, the three coal seams to-be-mined 1 are exploited for CBM by using stepped horizontal wells, and at the same time, the three coal seams to-be-mined 1 are exploited and drained by cluster wells until the coalbed methane mining is completed or has no economic mining value. As shown in FIG. 7 , three coal seams 1 to be mined are injected with gasification agent and ignited simultaneously through stepped horizontal wells to gasify the coal and form a coal gasification range 5, and the cluster wells are used for gas production. During the mining process, the generated gas is separated into carbon dioxide, and the separated carbon dioxide is injected into the lower coal seam and the middle coal seam through the well No. 1 41, and into the upper coal seam and the middle coal seam through the well No. 3 43. Since the simultaneous injection and production in the same wellbore is a relatively mature technology at present, its structure will not be repeated in this embodiment.

Embodiment 4

As shown in FIG. 8 , in this embodiment, there are three layers of coal seams to be mined 1, and adjacent coal seams to be mined 1 are separated by interlayers 2. Three second vertical wells 44 are used as production wells 4, and a stepped horizontal well is used as injection well 3. The stepped horizontal well has three horizontal sections: the first horizontal section 31, the second horizontal section 32 and the third horizontal section 33. The first horizontal section 31 is arranged in the upper coal seam to be mined, the second horizontal section is arranged in the middle coal seam to be mined, and the third horizontal section is arranged in the lower coal seam to be mined. For each horizontal section, there is a second vertical well 44 passing through the coal gasification range 5 of the coal seam to be mined 1 where the horizontal section is located.

As shown in FIG. 9 , firstly, three coal seams 1 to be mined are exploited for coalbed methane by using a stepped horizontal well. In this process, the three second vertical wells 44 are simultaneously exploited for coalbed methane and drainage until the coalbed methane is fully exploited or has no economical exploitation value. The simplified migration directions of CBM and CBM are indicated in the figure.

As shown in FIG. 10 , gasification agent is injected through injection well 3 and coal gasification is carried out: First, injecting gasification agent into the lowest coal seam to be mined and igniting for coal gasification and forming coal gasification range 5. During the coal gasification process, the generated gasification gas is mined through the second vertical well 44 on the far right. The generated gasification gas is separated from carbon dioxide, and the separated carbon dioxide is injected into the lowest coal seam to be mined through the second vertical well 44 on the far left. After the gasification of the lower gasification section is completed, the coal in the middle coal seam to be mined starts to be gasified. Repeat this until all three layers of coal to be mined have been mined. During the mining process, when the coal in the central coal seam to be mined is gasified, the separated carbon dioxide is injected through the second vertical well on the far right or on the far left. When gasifying the upper coal seam to be mined, carbon dioxide is injected through the second vertical well on the far right.

In essence, in the above embodiment, when reinjecting carbon dioxide, in principle, it is only necessary to inject carbon dioxide into the coal seam where the gasification section is located through different production wells. However, considering the need to exploit the coalbed methane as much as possible, when the injected carbon dioxide is too close to the coal gasification range, the carbon dioxide is easily recovered. Therefore, the injection wells far from the target coal gasification range are usually selected to inject carbon dioxide.

In the description of the present application, it should be noted that the terms “first”, “second”, “upper”, “lower”, “middle”, “left”, “right”, etc. which are used to indicate position or positional relationship are based on the position or positional relationship shown in the drawings, and are only for the convenience of describing the application and simplifying the description, rather than indicating or implying that the indicated position or element must have a specific orientation and be constructed in a specific orientation and operation, therefore cannot be understood as a limitation of the present application.

The above-mentioned embodiments are only part of the embodiments of the present application, and are used to describe the basic principles, implementation purposes and detailed processes of the present application, and do not limit the application scope of the present application. Any modifications, equivalent changes and amendments made to the above embodiments according to the technical essence of the present application, all belong to the scope of the technical solutions of the present application. The present application is disclosed above with preferred embodiments, but those skilled in the art should understand that these embodiments are only used to describe the present application and should not be construed as limiting the scope of the present application. Without departing from the principles of the present application, further improvements to the present application should also be considered within the protection scope of the present application. 

What is claimed is:
 1. An integrated method for in-situ hydrogen production from coal seams and coalbed methane exploitation, comprising the following steps: injecting gasification agent through an injection well, and exploiting coalbed methane and gasification gas through a production well; wherein the injection well is configured to be a stepped horizontal well, the injection well is provided with at least one, and the projections of the horizontal sections of any two injection wells in the vertical direction do not overlap, and at least one horizontal section of the stepped horizontal well is arranged in any coal seam to be mined.
 2. The method according to claim 1, wherein the production well is configured to be a cluster well, and a directional well or a first vertical well of the cluster well is configured to pass through all the coal seams to be mined.
 3. The method according to claim 1, wherein the production well is a combination of a plurality of second vertical wells or inclined wells, and the second vertical wells or inclined wells are configured to pass through all the coal seams to be mined.
 4. The method according to claim 2, wherein in any of the horizontal sections, a vertical well or inclined well passing through the coal seam to be mined where the horizontal section is located is provided in the coal gasification range of the horizontal section, and the horizontal section communicates or does not communicate with its adjacent vertical well or inclined well.
 5. The method according to claim 3, wherein in any of the horizontal sections, a vertical well or inclined well passing through the coal seam to be mined where the horizontal section is located is provided in the coal gasification range of the horizontal section, and the horizontal section communicates or does not communicate with its adjacent vertical well or inclined well.
 6. The method according to claim 1, wherein before injecting the gasification agent into the injection well and exploiting the coalbed methane and gasification gas through the production well, the method further comprises: draining water from the coal seam through the production well.
 7. The method according to claim 1, wherein multi-layered coal seams to be mined are simultaneously injected with a gasification agent and gasified simultaneously; or, starting from the lowest coal seam to be mined, the gasification agent is injected upward layer by layer and gasified in stages.
 8. The method according to claim 1, wherein after injecting gasification agent into the injection well, and after exploiting coalbed methane and gasified gas in the production well, the method also comprises: carrying out carbon dioxide separation on the ground from the mined coalbed methane and gasification gas, and injecting separated carbon dioxide into a target coal seam.
 9. The method according to claim 8, wherein the carbon dioxide is injected into the target coal seam through an injection well far from the horizontal section in the target coal seam.
 10. A structure for in-situ hydrogen production from coal seams and coalbed methane exploitation, comprising: an injection well, which is provided with at least one and is configured to be a stepped horizontal well, wherein the projections of the horizontal sections of any two injection wells in the vertical direction do not overlap, and at least one horizontal section of the stepped horizontal well is arranged in any coal seam to be mined; a production well, which is configured to pass through all the coal seams to be mined, and for any horizontal section of the injection well, there is a production well that passes through the coal gasification range of the coal seam where the horizontal section is located.
 11. The structure according to claim 10, wherein, the production well is configured to be a cluster well, and a directional well or a first vertical well of the cluster well is configured to pass through all the coal seams to be mined; or, the production well is a combination of a plurality of second vertical wells or inclined wells, and the second vertical wells or inclined wells are configured to pass through all the coal seams to be mined. 